Step 1

Preheat the oven to 350 degrees F and line a 9-inch square baking pan with parchment paper, allowing overhang on all sides.

Step 2

Cream the butter and sugar together in a bowl with an electric mixer until light and fluffy, about 3 minutes. Add the salt, vanilla and egg yolk and beat again until well mixed. Scrape down the sides of the bowl as needed. Gradually add the flour and mix well until combined and the dough comes together. Press evenly into the prepared pan, then poke holes over the entire surface with a fork. Bake until lightly browned and set, 23 to 25 minutes. Remove from the oven and allow to cool completely.

Step 3

Heat the caramels and sweetened condensed milk in a pot over medium heat, stirring constantly, until the caramels are melted but still thick and spreadable. Evenly spread the melted caramel over the cooled shortbread layer. Refrigerate until the caramel is fully set, about 30 minutes.

Step 4

For the chocolate ganache topping: To the bowl of a double boiler, add the chocolate chips and heavy cream, then continuously stir until the chocolate is melted and smooth. Spread the melted chocolate over the cooled caramel layer, then sprinkle the flaky salt on the chocolate and let sit at room temperature until the chocolate has set up, about 1 hour. Cut into bars and serve.